The present invention relates to a method of producing a sheet of grain-oriented electromagnetic steel, particularly a sheet of grain-oriented electromagnetic steel of such high grade that is high in terms of magnetic flux density and is small in term of watt loss.
A sheet of grain-oriented electromagnetic steel is produced by subjecting a sheet of hot-rolled silicon steel to more than one operations of cold rolling and more than one operations of annealing, so as to set the thickness of said sheet to a commercial standard, and then by subjecting said sheet to final high-temperature annealing at more than 1100.degree. C for more than 10 hours, so as to get abnormal growth of such grain that has the grain texture of (110) [001] according to Miller indices (such growth being called as the "secondary recrystallization"). The so produced grain-oriented electromagnetic steel sheet has the easiest magnetization axis oriented in the rolling direction, thus having excellent magnetic properties, so that is is used mostly as the iron core of a transformer. As the material for the iron core, it is required to be as small as possible in watt loss, as the consumption of thermal energy decreases as the watt loss decreases. Hence, demand is increasing for sheets of grain-oriented electromagnetic steel of high grade under the present situation where power production cost is increasing, and the saving of power consumption is advocated in view of decreasing energy reserves.
In order to reduce watt loss of such steel, the following means are taken:
1. Increase the content of silicon; PA1 2. Reduce the thickness of sheet; PA1 3. Reduce the content of impurities to a minimum; PA1 4. Raise the magnetic flux density by setting higher grain texture (110) [001] of grain; and PA1 5. make smaller grain steel sheets
Of the abovementioned means, higher magnetic flux density and smaller grain, can be secured only by the appropriate level of secondary recrystallization.
Even according to the prior art, it is theoretically concluded that the proper level of secondary crystallization can be secured by abnormal growth exclusively of crystal grain having the orientation (110) [001] by the presence of a dispersed phase consisting of such elements as selenium or stiblum and such compounds as sulfides, nitrides, selenides or antimonides (Examples: MnS; AlN; Se; Sb) as the inhibiter of normal grain growth in steel sheets before final high-temperature annealing, and also by a strong crystal texture produced in steel sheet.
However, in the practice of prior art, the methods for controlling the growth of secondary recrystallization grains results in poor control of normal grain growth, making it very difficult to obtain high grade grain-oriented electromagnetic steel sheets.